The present invention relates to a fault restoration control method and apparatus thereof in a communication network, and in particular to a fault restoration control method suitable for a communication network using an optical cross-connect equipment for changing over from one optical fiber to another by using an optical switch.
Conventionally, in the case where a communication network was to be formed by using an optical fiber as a signal transmission line, an optical-electric signal converter and a line terminal equipment were disposed so as to be associated with each optical fiber in a node equipment for controlling communication. In the case where a transmission line fault such as degradation of characteristics of an optical fiber or breaking of an optical fiber occurred, the line terminal equipment detected that fault and changed the optical fiber over to a protection system.
Furthermore, in recent years, an equipment adapted to change over one optical fiber over to another by using an optical switch and called optical cross-connect equipment is disposed in the node equipment together with the line terminal equipment, and a communication network is formed by using such node equipments.
FIG. 11 is a block diagram showing an example of a communication network using optical cross-connect equipments according to a reference technique. FIG. 12 is a block diagram showing the configuration of a node equipment. FIG. 13 is a sequence diagram illustrating restoration operation from a fault in the communication network. With reference to FIGS. 11 and 12, N1 through N3 denote node equipments, LTE1 through LTE3 denote line terminal equipments, OXC1 through OXC3 denote optical cross-connect equipments, OF12, OF13 and OF23 optical fibers, 60 a fault detector, 61 an OXC change-over trigger generator, 62 an OXC change-over control signal transfer section, 63 a communication controller with respect to its own node OXC, 64 a communication controller with respect to other nodes, 65 a change-over route determining section, 66 an optical switch controller, 67 a change-over trigger acceptance section, 68 an other node information collector, 69 an other node OXC change-over request section, and 6A a communication controller, and 6B is equipment's own node information sending section.
The communication network shown in FIG. 11 is formed by interconnecting the three node equipments N1 through N3 via the optical fibers OF12, OF13, and OF23 serving as signal transmission lines. Although the illustrated communication network has three node equipments, a larger number of node equipments may be disposed and interconnected via optical fibers. As this communication network, any communication network may be used so long as at least two node equipments are interconnected by interconnection between the node equipments or optical cross-connect equipments. Each of the node equipments N1 through N3 is formed by a line terminal equipment LTE and an optical cross-connect equipment OXC as shown in FIG. 12.
The line terminal equipment LTE has a control function of signal transmission between node equipments, and control functions such as commanding the optical cross-connect equipment to change one optical fiber over to another in response to degradation of characteristics of the optical fiber or breaking of the optical fiber. Specifically, the line terminal equipment LTE is formed so as to have the fault detector 60, the OXC change-over trigger generator 61, the OXC change-over control signal transfer section 62, the communication controller 63 with respect to its own node OXC, and the communication controller 64 with respect to other nodes, as shown in FIG. 12.
The optical cross-connect equipment OXC has a function of conducting a change-over of one optical fiber serving as a transmission line to another by switching an optical switch disposed therein in response to a command given by the line terminal equipment. Specifically, the optical cross-connect equipment OXC is formed so as to have the restoration route determining section 65, the optical switch controller 66, the change-over trigger acceptance section 67, the other node information collector 68, the other node OXC change-over request section 69, the communication controller 6A and equipment's own node sending section 6B as shown in FIG. 12.
The configuration of the line terminal equipment LTE and the optical cross-connect equipment OXC shown in FIG. 12 represents only a configuration required for restoration from a fault. As for functions for the normal signal transmission, functions similar to the reference technique are provided.
It is now assumed in the node equipments configured as described above and a communication network including such node equipments that a node equipment N1 and a node equipment N2 transmit and receive a signal via an optical fiber OF12 interconnecting them and the line terminal equipment LTE1 included in the node equipment N1 has detected occurrence of a fault in the optical fiber OF12. In this case, the line terminal equipment LTE1 exchanges control information for restoration from the fault with other node equipments, thereby collects node information of other node equipments, and delivers the collected node information of other node equipments to the optical cross-connect equipment OXC1. The optical cross-connect equipment OXC1 determines a transmission route, changes over the transmission line from the optical fiber OF12 to another optical fiber, and conducts restoration from the fault.
Such an operation for restoration from a fault will now be described by referring to a sequence shown in FIG. 13. It is now assumed that a fault has occurred in the optical fiber OF12 interconnecting the node equipment N1 and the node equipment N2 when the node equipment N1 and the node equipment N2 are transmitting and receiving signals via the optical fiber OF12, and a route is then formed between the node equipment N1 and the node equipment N2 as a restoration route via the optical fiber OF13, the node equipment N3, and the optical fiber OF23. FIG. 13 shows an example in such a case.
(1) Upon detecting the occurrence of a fault in the optical fiber OF12, the line terminal equipment LTE1 in the node equipment N1 requests the optical cross-connect equipment OXC1 included in its own node equipment to change over from the optical fiber OF12. Upon receiving this request, the optical cross-connect equipment OXC1 requests the line terminal equipment LTE1 to collect node information (steps 701 and 702).
(2) The line terminal equipment LTE1 requests line terminal equipments of other node equipments, i.e., the line terminal equipments LTE2 and LTE3 respectively of the node equipments N2 and N3 in this case, to transfer the node information (steps 703 and 704).
(3) Upon receiving the node information transfer request, the line terminal equipments LTE2 and LTE3 respectively of the node equipments N2 and N3 collects node information from the optical cross-connect equipments OXC2 and OXC3 of its own node equipment and transfer that node information to the line terminal equipment LTE1 (steps 705 through 710).
(4) The line terminal equipment LTE1 delivers the transferred node information of the node equipments N2 and N3 to the optical cross-connect equipment OXC1 included in its own node equipment as answer information. On the basis of each node information thus delivered, the optical cross-connect equipment OXC1 determines a restoration route thereto. Together with the route information thus determined, the optical cross-connect equipment OXC1 then transmits a change-over request to the line terminal equipment LTE1 (steps 711 through 714).
(5) The line terminal equipment LTE1 commands the line terminal equipments LTE2 and LTE3 respectively of the node equipments N2 and N3 to conduct change-over operations complying with the determined route information. Each of the line terminal equipments LTE2 and LTE3 commands the optical cross-connect equipment OXC2 or OXC3 included in its own node equipment to conduct the change-over complying with the command given by the line terminal equipment LTE1 (steps 715 through 718).
(6) Each of the optical cross-connect equipments OXC1 through OXC3 included in respective node equipments conducts optical switch change-over in its own equipment in order to form the determined route. This change-over is conducted by respective equipments in aligned timing. Furthermore, the optical cross-connect equipments OXC2 and OXC3 report the completion of the change-over to the line terminal equipment LTE1 of the node equipment N1 via the line terminal equipments LTE2 and LTE3 (steps 719 through 725).
(7) The line terminal equipment LTE1 of the node equipment N1 reports the completion of the optical fiber change-over in the optical cross-connect equipments OXC2 and OXC3 to the optical cross-connect equipment OXC1 included in its own node equipment (steps 726 and 727).
In the case where a fault has occurred in the optical fiber OF12, the restoration route connecting the ru node equipment N1 to the node equipment N2 via the optical fiber OF13, the node equipment N3, and the optical fiber OF23 can be formed owing to the above described processing.
By the way, in the above described processing, the processing for collecting the node information of other node equipments conducted by the line terminal equipment LTE1 at the steps 703 and 704 is conducted for all node equipments included in the communication network. The optical fiber change-over commands at the steps 715 and 716 are given to only the node equipments concerning the determined restoration route.
The above described processing is conducted by exchanging fault restoration control information between the node equipments by using headers of the Synchronous Digital Hierarchy (SDH) which is an international standard. In this case, the header portion cannot be analyzed in the optical cross-connect equipment OXC. Therefore, all of the control signals must be let flow via the line terminal equipment LTE as described above with reference to FIG. 13 and as represented by broken lines in FIG. 11.
In general, exchange of the fault restoration control information between the nodes using a header is conducted by using a data communication channel (DCC) included in the header. Instead, however, it may be conducted by using a different method, such as providing, between the node equipments, a network dedicated to control signals. In this case as well, however, the exchange of the control signal with another node equipment cannot be conducted without passing the control signal through the line terminal equipment LTE once. The control signal cannot be sent directly to the optical cross-connect equipment of another node equipment.
As described above, the exchange of the fault restoration control information between the nodes is conducted via the line terminal equipment in the reference technique. This aims at efficiently utilizing K1 bytes and K2 bytes already prepared in the header of the SDH to transmit the change-over signals between the line terminal equipments LTEs.
In the above described reference technique, the exchange of the fault restoration control information between the nodes is conducted via the line terminal equipment LTE. In the case where a node equipment lacking an equipment capable of interpreting the header of the SDH, such as the line terminal equipment LTE, exists as a node equipment in a communication network, the exchange of the control information with the node equipment cannot be conducted. For example, in the case where a node equipment formed by only the optical cross-connect equipment OXC exists as a node equipment in a communication network, the exchange of the control information with the node equipment cannot be conducted. The above described reference technique has such a problem.
In the above described reference technique, it is necessary to prescribe an interface between the line terminal equipment LTE and the optical cross-connect equipment OXC even in one node equipment. This causes an increase of an interface for exchanging the fault restoration control information. The above described reference technique thus has a problem of a complicated configuration of the node equipment.